A selective oxidation reaction of olefin occupies an important position in the petrochemical industry as a reaction capable of preparing an intermediate base material required for producing various products from an olefin raw material. A significant amount of research into a process of preparing styrene from ethyl benzene and a process of preparing 1,3-butadiene from n-butane or n-butene in the above reaction has been conducted as the recent demand for a base material for preparing a synthetic rubber has rapidly grown. In particular, since the demand for 1,3-butadiene has rapidly grown, there is a need to develop a technique for securing a sufficient amount of the 1,3-butadiene.
1,3-butadiene, a colorless and odorless flammable gas, is a material that is easily liquefied when the pressure is applied and is easily flammable, wherein it is a very important feedstock used as a raw material of various petrochemical products, for example, synthetic rubbers such as styrene-butadiene rubber (SBR), polybutadiene rubber (BR), and acrylonitrile-butadiene-styrene rubber (ABS).
As a method of preparing 1,3-butadiene, there are broadly naphtha cracking, direct dehydrogenation of n-butene, or oxidative dehydrogenation of n-butene. Among the above methods, the naphtha cracking responsible for 90% or more of 1,3-butadiene supplied to the market is performed in such a manner that 1,3-butadiene is selectively extracted from a feed stock which is produced from a cracker in a steam cracking process for the production of ethylene. However, since the main purpose of the steam cracking process is for the production of feedstocks other than 1,3-butadiene, the production of 1,3-butadiene by the steam cracking process may not be an effective process for producing 1,3-butadiene and a lot of energy consumption may be required due to a high reaction temperature. Accordingly, dehydrogenation has been received attention in which 1,3-butadiene is obtained by removing hydrogen from n-butene in a C4 mixture (C4 raffinate-3) which is remained after extracting all of the useful feedstocks in the steam cracking process. The dehydrogenation of n-butene includes direct dehydrogenation and oxidative dehydrogenation. The direct dehydrogenation of n-butene is a reaction of obtaining 1,3-butadiene by removing hydrogen from the n-butene, wherein the direct dehydrogenation has a limitation in that a high-temperature reaction condition is required due to a limited conversion rate because the direct dehydrogenation is thermodynamically unfavorable as a highly endothermic reaction, and the yield of 1,3-butadiene may be reduced because a side reaction, such as an idealized reaction, is increased due to an increase in the temperature even if the conversion rate is increased by increasing the temperature.
The oxidative dehydrogenation (ODH) of n-butene, which produces butadiene through the ODH of n-butene, is a reaction in which n-butene and oxygen are reacted to generate 1,3-butadiene and water, wherein the oxidative dehydrogenation of n-butene may not only be thermodynamically favorable because stable water is generated after the reaction, but may also obtain 1,3-butadiene with a high yield even at a lower reaction temperature than the direct dehydrogenation because it is an exothermic reaction different from the direct dehydrogenation. Thus, a process of producing 1,3-butadiene through the oxidative dehydrogenation of n-butene may be considered as an effective single production process which may meet the increasing demand of 1,3-butadiene.
As described above, since the oxidative dehydrogenation uses oxygen as a reactant even though it is an effective process capable of preparing 1,3-butadiene alone, the oxidative dehydrogenation may have a limitation in that a lot of side reactions, such as complete oxidation, occur. Thus, there is a need to develop a catalyst having high selectivity to 1,3-butadiene while maintaining high activity through the appropriate control of oxidation ability.
Current known catalysts used in the oxidative dehydrogenation of n-butene include a ferrite-based catalyst, a tin-based catalyst, and a bismuth-molybdenum-based catalyst.
Among the above catalysts, the bismuth-molybdenum-based catalyst includes a bismuth-molybdenum catalyst only composed of bismuth and molybdenum oxides and a multicomponent bismuth-molybdenum catalyst in which various metal components are added on the basis of bismuth and molybdenum. Various phases are present in a pure bismuth-molybdenum catalyst depending on an atomic ratio of bismuth to molybdenum, wherein it is known that three phases of α-bismuth molybdenum (Bi2Mo3O12), β-bismuth molybdenum (Bi2Mo2O9), and γ-bismuth molybdenum (Bi2MoO6) may be used as the above catalyst. However, a single-phase pure bismuth-molybdenum catalyst is not suitable for a commercialization process of preparing 1,3-butadien through the oxidative dehydrogenation of n-butene due to its low activity.
As an alternative, the preparation of a multicomponent bismuth-molybdenum catalyst, in which various metal components in addition to bismuth and molybdenum are added, has been attempted. Examples of the multicomponent bismuth-molybdenum catalyst may be a composite oxide catalyst composed of nickel, cesium, bismuth, and molybdenum, a composite oxide catalyst composed of cobalt, iron, bismuth, magnesium, potassium, and molybdenum, and a composite oxide catalyst composed of nickel, cobalt, iron, bismuth, phosphorous, potassium, and molybdenum.
The typical multicomponent bismuth-molybdenum catalyst as described above has been prepared by one-step co-precipitation of various metal precursors. However, in a case in which a multicomponent bismuth-molybdenum catalyst having complex components is prepared by one-step co-precipitation, the reproducibility of the preparation of the catalyst may not only be reduced because it may be difficult to uniformly form catalyst components, but economic efficiency may also be reduced because catalytic activity per unit mass may be reduced due to a low specific surface area of the catalyst. Also, in a case in which the reaction is performed in a temperature range of 320° C. to 520° C. or less, as a typical reaction temperature range, in order to increase the economic efficiency by reducing energy consumption, the catalytic activity may be reduced. Thus, in order to increase the economic efficiency, there is a need to develop a technique which may prepare a catalyst in which catalyst components are uniformly formed and its catalytic activity is not reduced under a relatively low temperature condition.
Under the above-described background, while conducting research into a method of preparing a catalyst which may appropriately control oxidation ability without a reduction in catalytic activity even at a relatively low temperature, the present inventors have confirmed that a multicomponent bismuth-molybdenum composite metal oxide catalyst, which is prepared by a method consisting of a two-step co-precipitation process that includes the steps of preparing a second solution by dropwise adding a first solution including a divalent or trivalent cationic metal precursor, a monovalent cationic metal precursor, and a bismuth precursor to a solution including a molybdenum precursor and performing primary co-precipitation; and dropwise adding a third solution including a tetravalent cationic metal precursor represented by Formula 2 and performing secondary co-precipitation, exhibits excellent catalytic activity even under a relatively low temperature condition while having the almost same structure as a typical quaternary bismuth-molybdenum catalyst, thereby leading to the completion of the present invention.